Reduce packet header size for point-to-point links

- new interface.x.point_to_point config
- disable local echo for point to point dummy interfaces
- add ME and YOU sid abbreviation codes after learning other sid

conf_schema.h

@@ -443,6 +443,7 @@ ATOM(bool_t,                send_broadcasts, 1, boolean,, "If false, don't send
 ATOM(bool_t,                default_route,   0, boolean,, "If true, use this interface as a default route")
 ATOM(bool_t,                prefer_unicast,  0, boolean,, "If true, send unicast data as unicast IP packets if available")
 ATOM(bool_t,                debug,           0, boolean,, "If true, log details of every outgoing packet")
+ATOM(bool_t,                point_to_point,  0, boolean,, "If true, assume there will only be two devices on this interface")
 ATOM(bool_t,                ctsrts,          0, boolean,, "If true, enable CTS/RTS hardware handshaking")
 ATOM(int32_t,               uartbps,         57600, int32_rs232baudrate,, "Speed of serial UART link speed (which may be different to serial device link speed)")
 END_STRUCT

overlay_address.c

@@ -39,6 +39,8 @@ static struct broadcast bpilist[MAX_BPIS];
 
 #define OA_CODE_SELF 0xff
 #define OA_CODE_PREVIOUS 0xfe
+#define OA_CODE_P2P_YOU 0xfd
+#define OA_CODE_P2P_ME 0xfc
 
 // each node has 16 slots based on the next 4 bits of a subscriber id
 // each slot either points to another tree node or a struct subscriber.
@@ -204,22 +206,37 @@ int overlay_address_append(struct decode_context *context, struct overlay_buffer
 {
   if (!subscriber)
     return WHY("No address supplied");
-  
-  if (context && subscriber==context->sender){
+
+  if(context
+      && context->packet_version>=1
+      && context->interface
+      && subscriber == context->interface->other_device
+      && context->interface->point_to_point){
+    if (ob_append_byte(b, OA_CODE_P2P_YOU))
+      return -1;
+  }else if(context
+      && context->packet_version>=1
+      && context->interface
+      && !subscriber->send_full
+      && subscriber == my_subscriber
+      && context->interface->other_device
+      && context->interface->point_to_point
+      && (!context->encoding_header || !context->interface->local_echo)){
+    if (ob_append_byte(b, OA_CODE_P2P_ME))
+      return -1;
+  }else if (context && subscriber==context->sender){
     if (ob_append_byte(b, OA_CODE_SELF))
       return -1;
-    
   }else if(context && subscriber==context->previous){
     if (ob_append_byte(b, OA_CODE_PREVIOUS))
       return -1;
-    
   }else{
     int len=SID_SIZE;
     if (subscriber->send_full){
       subscriber->send_full=0;
     }else{
       len=(subscriber->abbreviate_len+2)/2;
-      if (subscriber->reachable==REACHABLE_SELF)
+      if (context && context->encoding_header)
 	len++;
       if (len>SID_SIZE)
 	len=SID_SIZE;
@@ -328,6 +345,26 @@ int overlay_address_parse(struct decode_context *context, struct overlay_buffer
     return WHY("Buffer too small");
   
   switch(len){
+    case OA_CODE_P2P_YOU:
+      if (context->interface && context->interface->point_to_point){
+        *subscriber=my_subscriber;
+	context->previous=my_subscriber;
+      }else{
+	WHYF("Could not resolve address on %s, this isn't a configured point to point link", context->interface->name);
+	context->invalid_addresses=1;
+      }
+      return 0;
+
+    case OA_CODE_P2P_ME:
+      if (context->interface && context->interface->point_to_point && context->interface->other_device){
+        *subscriber=context->interface->other_device;
+	context->previous=*subscriber;
+      }else{
+	WHYF("Could not resolve address on %s, I don't know who is on the other end of this link!", context->interface->name);
+	context->invalid_addresses=1;
+      }
+      return 0;
+
     case OA_CODE_SELF:
       if (!context->sender){
 	INFO("Could not resolve address, sender has not been set");

overlay_address.h

@@ -106,7 +106,12 @@ struct decode_context{
   int packet_version;
   int encapsulation;
   struct sockaddr_in addr;
-  int invalid_addresses;
+  union{
+    // only valid while decoding
+    int invalid_addresses;
+    // only valid while encoding
+    int encoding_header;
+  };
   struct overlay_frame *please_explain;
   struct subscriber *sender;
   struct subscriber *previous;

overlay_interface.c

@@ -392,6 +392,7 @@ overlay_interface_init(const char *name, struct in_addr src_addr, struct in_addr
   interface->state=INTERFACE_STATE_DOWN;
   interface->alarm.poll.fd=0;
   interface->debug = ifconfig->debug;
+  interface->point_to_point = ifconfig->point_to_point;
 
   // How often do we announce ourselves on this interface?
   int tick_ms=-1;
@@ -469,12 +470,15 @@ overlay_interface_init(const char *name, struct in_addr src_addr, struct in_addr
     interface->address.sin_addr = src_addr;
     interface->broadcast_address.sin_addr = broadcast;
     interface->netmask = netmask;
+    interface->local_echo = 1;
     
     if (overlay_interface_init_socket(overlay_interface_count))
       return WHY("overlay_interface_init_socket() failed");
   }else{
     char read_file[1024];
     
+    interface->local_echo = interface->point_to_point?0:1;
+
     strbuf d = strbuf_local(read_file, sizeof read_file);
     strbuf_path_join(d, serval_instancepath(), config.server.interface_path, ifconfig->file, NULL);
     if (strbuf_overrun(d))
@@ -642,9 +646,12 @@ static void interface_read_file(struct overlay_interface *interface)
       
       if (config.debug.packetrx)
 	DEBUG_packet_visualise("Read from dummy interface", packet.payload, packet.payload_length);
-      
-      if (!should_drop(interface, packet.dst_addr)){
-	    
+
+      if (should_drop(interface, packet.dst_addr) || (packet.pid == getpid() && !interface->local_echo)){
+	if (config.debug.packetrx)
+	  DEBUGF("Ignoring packet from %d, addressed to %s:%d", packet.pid,
+	      inet_ntoa(packet.dst_addr.sin_addr), ntohs(packet.dst_addr.sin_port));
+      }else{
 	if (packetOkOverlay(interface, packet.payload, packet.payload_length, -1, 
 			    (struct sockaddr*)&packet.src_addr, sizeof(packet.src_addr))<0) {
 	  if (config.debug.rejecteddata) {
@@ -653,8 +660,7 @@ static void interface_read_file(struct overlay_interface *interface)
 	    dump("the malformed packet",packet.payload,packet.payload_length);
 	  }
 	}
-      }else if (config.debug.packetrx)
-	DEBUGF("Ignoring packet addressed to %s:%d", inet_ntoa(packet.dst_addr.sin_addr), ntohs(packet.dst_addr.sin_port));
+      }
     }
   }
   

overlay_packetformats.c

@@ -47,9 +47,10 @@ int overlay_packet_init_header(int packet_version, int encapsulation,
     return -1;
   if (ob_append_byte(buff, encapsulation))
     return -1;
-
+  context->encoding_header=1;
   if (overlay_address_append(context, buff, my_subscriber))
     return -1;
+  context->encoding_header=0;
   context->sender = my_subscriber;
   
   int flags=0;
@@ -258,7 +259,11 @@ int parseEnvelopeHeader(struct decode_context *context, struct overlay_interface
   IN();
   time_ms_t now = gettime_ms();
   
+  context->interface = interface;
+  context->sender_interface = 0;
+
   context->packet_version = ob_get(buffer);
+
   if (context->packet_version < 0 || context->packet_version > SUPPORTED_PACKET_VERSION)
     RETURN(WHYF("Packet version %d not recognised.", context->packet_version));
   
@@ -271,9 +276,6 @@ int parseEnvelopeHeader(struct decode_context *context, struct overlay_interface
   
   int packet_flags = ob_get(buffer);
   
-  context->sender_interface = 0;
-  context->interface = interface;
-
   int sender_seq = -1;
 
   if (packet_flags & PACKET_INTERFACE)
@@ -293,6 +295,11 @@ int parseEnvelopeHeader(struct decode_context *context, struct overlay_interface
     if (context->sender->max_packet_version < context->packet_version)
       context->sender->max_packet_version = context->packet_version;
 
+    if (interface->point_to_point && interface->other_device!=context->sender){
+      INFOF("Established point to point link with %s on %s", alloca_tohex_sid(context->sender->sid), interface->name);
+      context->interface->other_device = context->sender;
+    }
+
     // TODO probe unicast links when we detect an address change.
     
     // if this is a dummy announcement for a node that isn't in our routing table

overlay_queue.c

@@ -271,11 +271,13 @@ overlay_init_packet(struct outgoing_packet *packet, struct subscriber *destinati
 		    int unicast, int packet_version,
 		    overlay_interface *interface, struct sockaddr_in addr){
   packet->interface = interface;
+  packet->context.interface = interface;
   packet->i = (interface - overlay_interfaces);
   packet->dest=addr;
   packet->buffer=ob_new();
   packet->seq=-1;
   packet->packet_version = packet_version;
+  packet->context.packet_version = packet_version;
 
   if (unicast)
     packet->unicast_subscriber = destination;

serval.h

@@ -403,7 +403,13 @@ typedef struct overlay_interface {
   char prefer_unicast;
   // can we use this interface for routes to addresses in other subnets?
   int default_route;
+  // should we log more debug info on this interace? eg hex dumps of packets
   char debug;
+  char local_echo;
+
+  // can we assume there will only be two devices on this interface?
+  char point_to_point;
+  struct subscriber *other_device;
   
   /* Number of milli-seconds per tick for this interface, which is basically related to the     
    the typical TX range divided by the maximum expected speed of nodes in the network.

tests/routing

@@ -185,6 +185,28 @@ test_mismatched_encap() {
    tfw_cat --stdout --stderr
 }
 
+doc_single_p2p="Start 2 instances on a point to point link"
+setup_single_p2p() {
+   setup_servald
+   assert_no_servald_processes
+   foreach_instance +A +B create_single_identity
+   foreach_instance +A +B add_interface 1
+   foreach_instance +A +B \
+     executeOk_servald config \
+       set interfaces.1.debug 1 \
+       set interfaces.1.encapsulation single \
+       set interfaces.1.point_to_point on
+   foreach_instance +A +B start_routing_instance
+}
+test_single_p2p() {
+   wait_until path_exists +A +B
+   wait_until path_exists +B +A
+   assertGrep "$instance_servald_log" 'Established point to point link'
+   set_instance +A
+   executeOk_servald mdp ping --timeout=3 $SIDB 1
+   tfw_cat --stdout --stderr
+}
+
 doc_slip_encoding="Test slip encoding and decoding"
 setup_slip_encoding() {
    setup_servald